1. Field of the Invention
The present invention relates to an electrochromic display device of laminated construction and more particularly to such a device with an electrolyte which contains a contrast-enhancing adjuvant in order to intensify the contrast between the colourless and the coloured states of an electrochromic layer, and to a method of producing such a display device.
2. Description of the Prior Art
A display device of the above-mentioned type is already known from DT-OS 2,201,104. The display device described in this published specification contains a laminar electrolyte in contact with an electrochromic layer, preferably exhibiting a high protonic conductivity, to which a pigment, such as white titanium dioxide or a yellow titanate, is added in order to enhance the contrast between the coloured and colourless states of the electrochromic layer. However such pigments exhibit large specific surfaces so that the addition of the pigment to the electrolyte causes chemical impurities, more particularly water, to be introduced into the indicating device. Owing to these impurities a device of the above-mentioned type can only be operated with a low service voltage, so that the switching-over from the colourless to the coloured state, and vice versa, takes a very long time. To increase the service voltage, on the other hand, would reduce the useful life of the device very considerably.